The present invention relates generally to rotating electrical machines and in particular to synchronous rotating machines having a permanent magnet rotor.
A rotating machine whose rotor has a series of permanent magnets on the surface of the rotor or buried below the surface of the rotor to define an appropriate distribution of south and north poles is known in the art.
Because a machine of the above kind is permanently excited by the magnets, it is necessary to provide flux weakening arrangements, i.e. means for circulating a flux that does not cooperate magnetically with the stator windings, in particular if the machine is operating under low load conditions.
FIG. 1 shows a prior art solution to this problem with a rotor 20 which comprises magnets 22S defining south poles alternating with magnets 22N defining north poles. The prior art solution consists of placing between the magnets of each pair of adjacent magnets a magnetic flux weakening part 24 adapted to cooperate with the poles of the stator to provide the required flux weakening.
FIG. 2 is a developed view of the rotor cooperating with a stator 10 which has teeth 16 delimited by notches 14 housing stator windings 18. A stator flux FI is created by the magnets and there is an opposite flux weakening flux FD. The figure shows that the stator flux and the flux weakening flux are poorly individualized and it has been found that this partial superposition of the stator and flux weakening fluxes, which are in opposite directions, limits the flux weakening capacity of the machine.
A first object of the present invention is to alleviate this drawback.
Another object of the invention is to reduce the ripple affecting the torque when the machine is operating.
Accordingly, the present invention proposes a rotating electrical machine, in particular an alternator or combined alternator/starter motor for automobile vehicles, comprising a stator equipped with stator windings and a rotor mounted to rotate inside the stator, the rotor having a series of permanent magnets of alternating polarity juxtaposed with variable reluctance magnetic parts associated with respective permanent magnets, each combination of a permanent magnet and an associated magnetic part defining one rotor pole, characterized in that at least some of said poles have alternately, in a generally tangential direction, a permanent magnet followed by its magnetic part and a permanent magnet preceded by its magnetic part.
Preferred but non-limiting features of the rotating machine of the present invention are:
the rotor has, in said generally tangential direction, pairs of adjacent permanent magnets corresponding to poles n and n+1 alternating with pairs of adjacent magnetic parts corresponding to poles n+1 and n+2.
the permanent magnets are radial flux permanent magnets.
the permanent magnets are mounted on the surface of the rotor.
the permanent magnets are buried below the periphery of the rotor.
the permanent magnet and the associated magnetic part in the same pole have similar dimensions in said circumferential direction.
the permanent magnets have a generally triangular shape and two successive permanent magnets are oriented head-to-tail.
the poles of the rotor are defined by interleaved pole claws of two rotor parts.